Some experiments were carried out on the beech and spruce lignin isolated with aqueous xylenesulfonate solution, designated “hydrotropic lignin”. The lignin thus obtained has been considered by some investigators to be one of the lignin preparations whose properties are little changed from those of the protolignin. The results of the authors' experiment, however, show that there is a marked difference between them. The results may be summarized follows. (1) Solubilites in several solvents of the isolated lignin were fairly well and were similar to those of alkali lignin and phenol lignin. But in the phloroglucinol-hydrochloric acid reaction, the beech lignin was negative and the spruce lignin was faintly positive. In the Mäule reaction the beech lignin was negative, too. (2) The methoxyl content of the beech lignin was 16.2_??_16.9% and that of the spruce lignin was 10.8_??_12.0%. This indicates that same of methoxyl groups existing in the original lignin were splitted in the isolating process. The methoxyl content of fully methylated lignin, which were prepared by methylation of the isolated lignins with diazomethane and then by methylation of the resulting products with dimethylsulphate and sodium hydroxide, were 26.6% in the case of beech and 20.8% in spruce. These figures indicates that some of free hyproxyl groups in lignin were blocked up during the isolation, due to selfcondensation between lignins and condensation between lignin and degraded products from carbohydrates. (3) The dissolution of lignin with xylenesulfonate cooking may take place in two steps. In the first step the lignin is changed by the action of hot water in high temperature, and in the second step the lignin so altered is dissolved in the xylenesulfonate regant.